408 small block. A mild build, roller cam, EQ magnum heads, Mopar M-1 intake. Made 420 HP, 450 lb/ft on dyno. Blows blue smoke, lots of it. Inside of tail pipes are oily. Plugs don't look too bad, and engine runs well. I pulled intake and checked alignment, all was well. Intake ports were clean. Heads are brand new as are valves etc.. I'm at my wits end with this thing. It smokes at idle and upon deceleration from a higher speed, then on to gas gives a big puff of BLUE smoke. So its definetly burning oil.
I'm going to try changing valve seals. Opinions? Any chance rings are not seated, even though makes good power? Thanks!

try doing a leak down test it sounds like the rings didnt seal or it could be seals ,were they replaced upon rebuild.?

The fact that you mention deceleration and then smoke when you hit the gas makes me suspect the valve seals. Did you use umbrella seals or viton?

Builder used new viton valve seals.

Sorry this happened to you, I just fired a fresh engine, and you always worry about crap like this happening. Luckily mine is fine. I'm not calling your builder a liar, but I would pull a valve cover and check to make sure those new viton seals are actually there. Maybe whoever assembled them forgot? Good luck to you, I hope it is just the valve seals, as you can do those with the engine assembled.

Interesting read Robert, thanks for the link. As engine was run on builders dyno I suspect he ran it pretty hard, but I wasn't present. The printout he gave me showed he ran the engine to 5900 rpm's The power peaked at 4900 rpm's.

I went through the same thing with my s/block pumping oil out of the exhaust, did a compression and leak down test- OK, suspected unseated rings and faulty intake gasket sealing, finally change the valve stem seals and smoking problem was corrected. Good luck

I read the break-in article, but if applied to our motors, it doesn't take one thing into consideration....the cam break-in. I've always read you should break in your new engine at 20-30 minutes at 2000 rpm to keep from wiping the cam. Hard acceleration/decceleration is not possible using this technoque. What do you guys think?

It could also be a bad Intake Gasket , the Oil is getting sucked through the port , if the Heads have been Surfaced and the Block was Decked sometimes the Intake will not seal properly , check the Intake Gasket when you / if you pull it off. But the Leakdown Test that was Mentioned is a good way to tell what is going on.

You said the intake ports were clean. How did the backs of the valves look. If they were coated with black tarry looking stuff, it's bad valve stem seals. If they were as clean as the runners, you have a ring problem. Leak down test will tell you for sure. Even a new motor with rings yet to seat should not be smoking like a chimney.

Leakdown test might now show it if his oil control rings are not properly installed or broken in, the compression rings may be good and hide it.

what about the fuel?i have a 440 rebuilt thought there was major problems. white smoke sometimes blue smoke sometimes. turned out bad fuel drained tank,cleaned fuel system now not a puff. i think the ethanol in old gas really turns bad fast.

Years ago I had a fresh small block chevy that would run strong and hard on acceleration with no smoke but when I let off the throttle it would let out a cloud of smoke. I did a compression test that came out good so I added the umbrella seals and still had the same problem. I took the heads off and had them gone over again put them back on still had the problem. unfortunately I never rolled the motor over with the heads off. Finally took the motor out tore it down and found the wrist pin in the #1 piston had worked itself out and dug a 3/4" wide trench in the wall the length of the stroke. My theory was that on decel the oil would slosh to the front of the pan and fill the trench making the smoke. Why didn't it show up on a compression test???? hmmm Why was the #1 piston covering the trench when the heads were off????? maybe that's Why I'm on a MOPAR forum now

Do you have a picture of the cylinder walls before the ehads went on? If not, can you find out what the honing stone combination used on your engine by the shop was? Smoking is usually one of three things: Intake fitment and you'll see the marks and oil in the ports and it will smoke all the time, worse on deceleration. Intake valve guide/seal issues and as said you'll see it on the backside of the intake valve and the piston top and again, worse on cold starts and deceleration. Last is ring seal... You can tell by looking at the hone finish if it's too rough for modern rings. Top rig seals compression and should seat during cam break in. Second ring is the main oil scraper and should seat shortly after cam break in. Oil rings remove the major oil off the walls and they may take a few miles to seat. If the rings are bad, you'll see it in the leakdown. Symptoms are smoking all the time, excessive blowby showing out the breather/pcv grommets when running (oil in breather or wet oil in PCV) and PCV disconnected from carb (plug vacuum nipple on baseplate) and oil on the piston tops.

OK, thought I would update so maybe others can learn from this. I replaced all the valve seals with Viton seals, it had those white teflon seals on it. No more smoke, and it runs great. Don't know what the problem was with those others being a new engine and all. Thanks everyone with the input. This forum is such a valuable resource for all involved.